Apolipoprotein E (apoE) is a well-known lipid-binding protein that plays a main role in the metabolism and transport of lipids. More recently, apoE-derived peptides have been shown to exert antimicrobial effects. Here, we investigated the anti-bacterial activity of apoE using in vitro assays, advanced imaging techniques, and in vivo mouse models . The formation of macromolecular complexes of apoE and endotoxins from Gram-negative bacteria was explored using gel shift assays, transmission electron microscopy , and circular dichroism spectroscopy followed by calculation of the α-helical content. The binding affinity of apoE to endotoxins was also confirmed by fluorescent spectroscopy detecting the quenching and shifting of tryptophan intrinsic fluorescence. We showed that apoE exhibits antibacterial activity particularly against Gram-negative bacteria such as Pseudomonas aeruginosa and Escherichia coli. ApoE protein folding was affected by binding of bacterial endotoxins components such as lipopolysaccharide (LPS) and Lipid A , yielding similar increases in apoE αhelical content. Moreover, high molecular-weight complexes of apoE were formed in the presence of LPS, but not to the same extent as with Lipid A. Together, our results demonstrate that interaction of apoE with Gram-negative bacteria and their endotoxins leads to the structural changes in apoE and the formation of aggregate-like complexes. The protein interaction provides a molecular explanation for the observed antimicrobial effects of apoE, which binds to LPS on the bacterial surface and leads to cell membrane damage and bacterial death.

中文翻译：

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全长载脂蛋白 E 在清除革兰氏阴性菌及其内毒素中的作用。


载脂蛋白E（apoE）是一种众所周知的脂质结合蛋白，在脂质代谢和转运中起主要作用。最近，apoE 衍生肽已被证明具有抗菌作用。在这里，我们使用体外测定、先进成像技术和体内小鼠模型研究了 apoE 的抗菌活性。使用凝胶位移测定、透射电子显微镜和圆二色光谱法探索了 apoE 和革兰氏阴性细菌内毒素大分子复合物的形成，然后计算 α 螺旋含量。 apoE 与内毒素的结合亲和力也通过荧光光谱检测色氨酸内在荧光的猝灭和移动得到证实。我们发现 apoE 具有抗菌活性，特别是针对革兰氏阴性菌，如铜绿假单胞菌和大肠杆菌。 ApoE 蛋白折叠受到脂多糖 (LPS) 和脂质 A 等细菌内毒素成分结合的影响，导致 apoE α 螺旋含量类似增加。此外，apoE 的高分子量复合物在 LPS 存在下形成，但程度与脂质 A 不同。 总之，我们的结果表明 apoE 与革兰氏阴性细菌及其内毒素的相互作用导致结构变化apoE 和聚集样复合物的形成。蛋白质相互作用为观察到的 apoE 抗菌作用提供了分子解释，apoE 与细菌表面的 LPS 结合，导致细胞膜损伤和细菌死亡。